The present invention relates to an optical switching device and to a method of controlling the device. The device and the method are intended to be used in an optical transmission network.
Prior art optical transmission networks using optical switching include nodes provided with fast optical signal switching devices for switching data or groups of data of fixed or varying size. The transmitted groups of data are usually referred to as xe2x80x9cpacketsxe2x80x9d in the case of the Internet or xe2x80x9ccellsxe2x80x9d in the case of an ATM network. The field of the present invention includes not only packet switching but also circuit switching.
Optical switching consists of switching data, usually in the form of amplitude modulation of an optical carrier wave, from one optical link to another, preserving its optical nature, i.e. without converting it to the electrical domain. The switching is effected by optical switching devices including a photonic switching matrix. In the case of packet switching, these devices both switch the data and synchronize the packets, in order to manage conflicts so as to minimize losses of packets or data.
In the context of optical telecommunication networks using wavelength division multiplexing (WDM), the matrices are also intended to take account of the spectrum of the signals to be switched, i.e. they include spectrum selection and/or reallocation means using wavelength conversion and selection devices.
Optical switching devices include a number of optical components such as couplers, space switches, optical gates based on semiconductor amplifiers, optical delay lines and, in a WDM context, multiplexers/demultiplexers and tunable or non-tunable laser sources.
Switches must provide a required level of performance in terms of the bit error rate (BER) or the rate of loss of packets in the case of packet switching (complete loss of packets occurs when no physical resource is available for routing packets). This implies quality constraints on the components used such that any optical path in a switch, achieved by cascade coupling and/or activating a plurality of selected components, conforms to the required level of performance.
One prior art solution to this problem consists, when fabricating the device, of sorting the components and retaining only those that offer the best performance, which greatly reduces the fabrication yield and necessitates costly testing. This drawback is particularly critical in the frequent situation in which the components are fabricated in the form of strips grouping together a number of basic components such as lasers or optical gates. Rejecting a single component then leads to rejection of the entire strip.
Another solution is to sort the components and then place them selectively in the device so that any path includes not more than one component offering relatively poor performance, for example. However, this also penalizes the fabrication time and therefore the fabrication cost.
The object of the present invention is therefore to provide an optical switching device whose performance is acceptable, in particular in terms of the bit error rate, and consistent, regardless of the switching state of the device, without necessitating a rigorous sorting or a specific disposition of the components or hardware redundancy.
To this end the present invention proposes an optical switching device including:
an optical switching matrix including:
input ports,
output ports,
switching means between said input ports and said output ports, and
control means for said switching matrix,
xe2x80x83wherein said switching means include a space switch having inputs coupled to respective input ports and outputs coupled to spectrum selector stages, the states of the space switch and the spectrum selector stages thus defining optical paths between said input ports and said output ports so that incoming data at one of said input ports can be selectively switched to any of said output ports,
which device is characterized in that it includes at least one configuration table in which is written data identifying authorized optical paths ensuring a transmission error rate lower than a predetermined value and said control means cooperate with said configuration table to authorize only states of the space switch and the spectrum selector stages corresponding to authorized optical paths.
Thus a device according to the invention can be fabricated from available components, without rigorous preselection or special dispositions of the components. It is sufficient to determine, after installing the components, the optical paths offering insufficient performance and to exclude them from the configuration table. In this way, the control means can take this information into account and route switch data only to predetermined authorized paths, which ensures a required level of performance.
The configuration table can be programmed during fabrication and can also be modified during operation of the device, by means of regular updates, to take account of the evolution of the device in operation. For example, if aging causes deterioration of the characteristics of some components, making the performance of some paths inadequate, it is then sufficient merely to modify the configuration table accordingly.
The invention exploits the fact that the transmission resources (wavelengths, bands of wavelengths, fibers, or times in the case of packet switching) can be xe2x80x9cnon-dedicatedxe2x80x9d at the output, i.e. not strictly tied to specific destinations of the signals to be transmitted in the network. In other words, the invention offers the possibility of prohibiting the worst paths although, because of the non-dedication of resources, they are not strictly indispensable for the information to reach the respective destinations.
There is advantageously at least one authorized optical path between each input port and each output port. This avoids excessively limiting the functionality of the device.
One advantageous embodiment includes configuration tables corresponding to respective different classes of quality of service.
Furthermore, the switching means can include wavelength converter stages coupled to the downstream side of said spectrum selector stages.
One advantageous embodiment includes wavelength converter means at the input of said matrix.
Other features and advantages of the present invention will become more apparent in the course of the following description of one embodiment of the present invention, which is given by way of illustrative and nonlimiting example.